The present invention relates to a multilayered printed circuit board applicable to vast integration of semiconductor and a manufacturing method thereof.
Currently, a highly integrated assembly board has been required accompanied with the demands for higher integration, more pins and lower weight of a semiconductor device. In order to accomplish these demands, research and development for multiplying the layers of a circuit board and improving the circuit integration have been made.
As a method for multiplying the layers, a so-called building up method has been developed and is widely used. The method consists of laminating an insulating layer and a circuit layer in which the connection between these layers is accomplished by photoetching the insulating layer, forming via holes and then forming a plating layer on the surface. In some cases, a laser is used for forming the via holes.
Japanese laid open publication No. Hei 8-264971 discloses a manufacturing method of a multilayered printed circuit board using a building up method. The manufacturing method of this application is simply explained referring FIG. 9 as mentioned below.
At first, the first resin layer 53 is formed in range 52 where any pattern is not formed on internal board 51 having internal conductor pattern 50. The first resin layer 53 is formed so that prescribed clearance 54 is made between the lateral of internal conductor pattern 50 and the first resin layer 53. Next, the second resin layer 55 composing an insulating layer by coating and then hardening resin varnish. The second resin layer 55 fills up clearance 54 and covers internal conductor pattern 50 and the first resin layer 53. Then, adhesive layer 56 is formed on the second resin layer 55 followed by roughening. After that, outer conductor pattern 57 is formed on adhesive layer 56 be electroless plating.
However, the above-mentioned multilayered printed circuit board by building up method has the following problems to be solved.
Namely, in the above-mentioned method, when a multilayered printed circuit board is manufactured by laminating outer conductor pattern 57 on both sides of internal board having internal conductor pattern 50, complicated processes such as formation of the first resin layer 53, formation of the second resin layer 55 by coating and then hardening resin varnish, and further formation of adhesive layer 56 are required. For this reason, the reduction of cost of a multilayered printed circuit board using the building up method could not be attained.
There is another manufacturing method of multilayered printed circuit board in which metal thin film is formed by vaporizing.
However, the method has a problem that when the film is thin (a few xcexcm), pores are easily caused, while when the film is thick (10 xcexcm or more), the productability is deteriorated, which causes high cost.
The present invention aims to solve such problems. The objective of the present invention is to produce a clad sheet for printed circuit board which can be manufactured at low cost and has excellent properties, a multilayered printed circuit board using thereof and a manufacturing method thereof.
The clad sheet for printed circuit board according to the present invention is characterized in that it is manufactured by press-bonding a copper foil and a nickel foil at a reduction rate of 0.1 to 3%.
The clad sheet for printed circuit board according to another embodiment is characterized in that it is manufactured by press-bonding a copper foil of which one side or both sides have nickel plating layer and another copper foil or a copper foil of which one side has nickel plating layer.
The clad sheet for printed circuit board according to another embodiment is characterize in that it is a five-layered sheet comprising layers of copper/nickel/copper/nickel/copper.
The multilayered printed circuit board according to another embodiment is characterized in that it comprises:
a base having an internal conductor layer formed by selectively etching the clad sheet for printed circuit board as described above,
an insulating layer and an outer conductor layer formed on the surface of said base,
said outer conductor layer being made patterning, and
the internal conductor layer and the outer conductor layer being electrically connected by interposing a columnar conductor formed in said base by etching.
The manufacturing method of a multilayered printed circuit board according to the present invention is characterized in that it is comprising:
forming a clad sheet for printed circuit board by laminating a copper foil serving as a conductor layer and a nickel foil or nickel plating serving as an etching-stopper layer and by simultaneously press-bonding both at the reduction raze of 0.1 to 3%,
producing a base by selectively etching said multilayered clad street,
forming an insulating layer and an outer conductor layer or the surface of said tease,
making patterning said outer conductor layer, and
electrically connecting the internal conductor layer end the outer conductor layer by interposing a columnar conductor formed in said tease by etching.
The manufacturing method according to another embodiment is characterized in that:
said clad sheet for printed circuit board is formed by laminating said copper foil and said nickel foil or nickel plating and cold-press-bonding both at the reduction rate of 0.1 to 3% after contacting surfaces or said copper foil and said nickel foil or nickel plating are previously activation-treated in a vacuum chamber, and in that case,
said activation treatment is carried out
(1) in a hyper low pressure inert gas atmosphere of 1xc3x9710xe2x88x921 to 1xc3x9710xe2x88x924 Torr,
(2) by glow-discharging charging alternate current of 1 to 50 MHz between an electrode A consisting of said copper foil and said nickel plating having contacting surface which are electrically grounded respectively end other electrode B insulatingly held, and
(3) by sputter-etching
(4) in the manner that the area of the electrode exposed in plasma generated by said glow-discharging is no more than ⅓ the area of electrode B.